Hitherto, for instance, a rotary encoder has been used to detect the revolution angle and revolution speed of a motor or the like; rotary encoders are mainly classified as incremental encoders and absolute encoders. In the incremental encoder generates pulses of the number corresponding to the number of divided sections which are obtained by dividing one revolution range of a motor or the like at regular intervals, and a signal processing circuit counts the number of pulses, so that the rotational position or revolution speed of the motor or the like can be determined. The incremental encoder ordinarily outputs pulse signals of two phases, A and B, having a phase difference of 90.degree.; the direction of rotation (forward rotation or reverse rotation) of the motor or the like is discriminated by the phase relation (advance or delay). On the other hand, generally, one origin pulse (Z-phase pulse signal) is output during one revolution as a reference signal indicative of one revolution. The absolute encoder uses a code plate in which the absolute position in one revolution range of a motor or the like is expressed by a binary code. A parallel output type, an output type of A and B phases, and the like are known as output types. On the other hand, there are also an absolute encoder of the memory backup type in which the number of revolutions of a motor or the like is recorded by using a memory which uses a battery as a backup power source and an absolute encoder of the multi-rotation type in which an absolute position of one revolution or more of a motor or the like is also produced by using a reduction mechanism using a gear or the like.